The common city pigeon, a descendant of the wild Rock Dove, thrives in human-dominated environments due to its highly adaptable and opportunistic diet. These birds consume a wide variety of items, from seeds and grains to discarded human food scraps. This broad diet has led to curiosity about their habit of consuming earth materials, which is a targeted ingestion of non-food substances to supplement their nutritional intake.
Geophagy in Pigeons
Pigeons, along with many other bird species, intentionally consume soil, earth, or clay in a practice known as geophagy. This behavior is a well-documented phenomenon across the Columbidae family, which includes doves and pigeons. While the behavior is more pronounced in wild populations that rely on natural mineral licks, it persists even in urban birds.
Geophagy is distinct from random pecking because it is a deliberate search for specific types of earth, often containing high concentrations of particular mineral compounds. This ingestion of earth is driven by a physiological need that their regular diet does not satisfy. The consumed materials are not selected for their caloric value or for the purpose of mechanical digestion.
Nutritional and Detoxification Roles
One primary reason pigeons seek out clay is for mineral supplementation, particularly sodium and calcium, which are often limited in a seed-heavy diet. Sodium is a necessary electrolyte for nerve and muscle function, and its concentration in the plants pigeons eat is often very low. Similarly, calcium is needed for bone strength, proper nervous system function, and eggshell formation, especially in breeding females.
The second major function of clay consumption is detoxification, which relies on a chemical property called cation exchange capacity (CEC). Certain types of clay, such as bentonite or montmorillonite, have a high CEC, meaning they have a net negative electrical charge that allows them to attract and bind to positively charged ions. This binding mechanism allows the clay to adsorb toxins, such as bitter secondary compounds like tannins and alkaloids found in certain seeds or unripe fruits, before they can be absorbed into the bloodstream. By binding to these harmful substances, the clay effectively neutralizes them, protecting the bird’s digestive tract from irritation and allowing the toxins to pass safely through the system. This protective action essentially increases the pigeon’s dietary breadth, making otherwise slightly toxic foods safe to eat.
Distinguishing Clay from Digestive Grit
It is important to differentiate the chemical benefits of geophagy from the mechanical function of consuming grit. Grit consists of small, hard, insoluble particles like crushed stone, granite, or sand. Pigeons swallow grit solely for a physical purpose: it is stored in the gizzard, or ventriculus, a powerful muscular stomach.
In the gizzard, the ingested grit acts like a set of internal “teeth,” grinding and crushing tough, whole seeds and grains that the pigeon swallows. This mechanical action is necessary because pigeons lack actual teeth to break down the hard outer casings of their food. Clay particles, being much finer and sometimes soluble, cannot fulfill this grinding role. Therefore, a pigeon requires both: insoluble grit for physical digestion and specific mineral-rich clay or soil for chemical and nutritional balance.
How Urban Pigeons Access Minerals
In cities, pigeons rarely have access to natural clay licks or salt deposits, forcing them to adapt their geophagy to the urban landscape. They satisfy their mineral requirements by foraging on human-made structures and waste. For instance, they are frequently observed pecking at mortar and concrete, which are rich in calcium carbonate derived from limestone. The need for sodium is often met by consuming residue from road salt used for de-icing or by ingesting soils contaminated by salt-rich runoff. This urban foraging, while meeting a biological need, carries a risk of consuming contaminated materials that may contain heavy metals or other urban pollutants.